WASHINGTON (Reuters) - U.S. Senator Rand Paul, a conservative maverick who helped kill the latest Republican effort to overturn Obamacare, took issue with President Donald Trump's tax plan on Monday, asking in a tweet if it was really Republican.

"This is a GOP tax plan? Possibly 30 percent of middle class gets a tax hike? I hope the final details are better than this," the Kentucky Republican said in a statement on Twitter. He cited the results of a recent analysis by the nonpartisan Tax Policy Center think tank.

Paul's message could signal difficulties for tax reform in the Senate, where Republicans hold only a 52-48 majority over Democrats and have failed this year to overturn the 2010 Affordable Care Act, popularly known as Obamacare. Last week, Republican Senator Bob Corker told reporters he would not vote for tax legislation if it raises the deficit.

Trump and top Republicans in Congress say the tax plan they released last week will deliver a big tax cut to middle-class families and to businesses, and simplify the law by doing away with myriad deductions, loopholes and tax breaks.

But the Tax Policy Center found that many upper middle-income professionals and business people would see their tax bills go up from the loss of deductions.

Trump economic adviser Gary Cohn and Treasury Secretary Steven Mnuchin have also acknowledged that some people could see a tax hike.

Republican Kevin Brady, chairman of the tax-writing House of Representatives Ways and Means Committee, pushed back on the center's analysis and said Paul was basing his opinion on a report the U.S. representative dismissed as incomplete.

"Look, I love Rand Paul. He and I play baseball together as well, and he's a friend," Brady said on Monday. "(But) this is not the group you go to ... they have none of the key details that would allow an objective, complete analysis."

Brady, a member of the "Big Six" tax negotiators from Congress and the Trump administration who produced the framework, declined to say whether every American would see a tax cut from the plan.

But he added: "I will guarantee we are going to work hard to lower taxes on every American, increase their paychecks and dramatically simplify the code for them."